"Six weeks to save the euro," European leaders promised the world in September. That deadline passed at last week's Cannes G-20 summit with the goal looking further away then ever. Nothing of substance was agreed on the French Riviera to aid the cause of euro survival, but one giant decision was taken that could hasten its demise. Angela Merkel and Nicolas Sarkozy's announcement that Greece is free to leave the euro has transformed the nature of the euro.